The present invention relates generally to industrial robots, and more particularly to an industrial robot which allows its arms to be manipulated with a minimum of effort and precision.
A prior art industrial robot, as shown and described in Japanese Utility Model No. 59-41033, has a hydraulically operated, vertically swingable arm with a spray gun attached to it to perform paint spray operations in accordance with instructions stored in a memory. The instructions are initially taught by manipulating the robot arm so that the spray gun is located exactly in positions where paint is applied and translating the robot arm into position data for storage into the memory. In playback, the memory is addressed to successively read the stored position data to modulate the hydraulic pressure to move the robot arm along the intended path.
Another prior art industrial robot, which is a more recent and general type of industrial robot, employs an electric motor which directly drives the robot arm and a serve-control system which controls the motor in accordance with a difference which exists between a target position and the actual position of the arm. However, in this prior art, the servo-control system is designed to operate at all times and therefore it causes the robot arm to present a substantial amount of resistance to manual effort when it is desired to move it to a teaching position. As a result, it is difficult to achieve precision teaching control.